Axle assembly with cooling pump

ABSTRACT

An axle assembly with a cooling pump. The cooling pump includes a disk-shaped wheel with a plurality of radially-spaced ducts formed therein. The wheel is positioned in proximity to the axle assembly and rotated, allowing the ducts to draw air therethrough and direct the air to the axle assembly.

BACKGROUND OF THE INVENTION

The present invention generally relates to drive line power transfermechanisms and more particularly, to drive line power transfermechanisms that include a cooling system.

Modern vehicles typically include an axle assembly having a housing anda differential assembly. The housing includes a cavity into which thedifferential assembly is rotatably disposed. The differential assemblyis mechanically coupled to the vehicle's engine by a drive shaft. Thedifferential assembly is also coupled to the vehicle drive wheels via apair of axle shafts. The differential assembly regulates the drivetorque between the axle shafts thereby causing the shafts to rotate.During operation of the vehicle, friction between the various componentsof the differential assembly generates heat, which if unabated coulddecrease the useful life of the axle assembly. A lubricating fluid,which is contained within the cavity of the axle assembly is thereforetypically employed to remove heat from the various components of thedifferential assembly. The lubricating fluid then rejects, or transfers,this heat to the housing, which, in turn, rejects or transfers this heatvia convection, conduction, and radiation to the environment in whichthe vehicle is operating.

Current advances in the fuel efficiency of vehicles have resulted indecreased air flow under the vehicle, which significantly reduces thecapability of the housing of the axle assembly to reject heat.

One solution that has been suggested utilizes a dedicated heat exchangerfor removing heat from the housing of the axle assembly. Severaldrawbacks have been noted with this approach, however. For example, theviscosity of the lubricating fluids in an axle assembly is such that thelubricating fluid is relatively difficult to pump, particularly when theambient air temperature is relatively low. Another drawback concerns thecost of the pumps and heat exchangers used in these systems.

In view of the aforementioned drawbacks, there remains a need in the artfor an axle assembly having a cooling system that provides improvedcooling of the axle lubricant and axle assembly components.

SUMMARY OF THE INVENTION

In one preferred form, the present invention provides a axle assemblyhaving a housing, a power transfer mechanism and a fluid. The housinghas a wall member that defines a cavity. The power transfer mechanism ispositioned within the cavity. The fluid extracts heat from the powertransfer mechanism during operation of the drive line power transferassembly. The fluid transfers the heat to the wall member via an insidesurface of the wall member and the wall member transfers this heat tothe ambient air via the outside surface of the wall member. The axleassembly further includes an wheel located outside the housing which isoperably coupled to the power transfer mechanism for rotation therewith.The wheel includes at least one duct that is adapted to pump air to theoutside surface of the differential thereby increasing the coolingcapacity associated with the power transfer assembly.

In another form the present invention provides a generally solid bodybounded by an annular leading surface, an annular trailing surface, andan outer surface, wherein the leading surface and the trailing surfaceare generally parallel, the body having a central bore and a pluralityof radially spaced apertures extending therethrough from the leadingsurface to the trailing surface wherein the central bore is adapted torestrain the wheel for rotation with a shaft and the radially spacedapertures are adapted to draw a fluid therethrough during said rotation

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional advantages and features of the present invention will becomeapparent from the subsequent description and the appended claims takenin conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of an exemplary motor vehicle into whichthe axle assembly constructed in accordance with the teachings of thepresent invention is incorporated;

FIG. 2 is a schematic view of the drive train of the motor vehicle ofFIG. 1;

FIG. 3 is a plan view of the differential portion of an axle assembly ofthe drive train in FIG. 2;

FIG. 4 is a side view of the differential of FIG. 3;

FIG. 5 is a perspective view of the wheel shown in FIG. 3;

FIG. 6 is a side view of the wheel of FIG. 5;

FIG. 7 is a front view of the wheel of FIG. 5;

FIG. 8 is a plan view of a conventional duct within a streamline body;

FIG. 9 is a sectional view taken along line 9-9 of FIG. 8; and

FIG. 10 is an alternate embodiment of the wheel of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. In particular, the present invention isdirected to an improved axle assembly of the type used in motor vehicledrive train applications. The axle assembly of the present inventionincludes a cooling pump to pump air to the outside of the differentialassembly thereby lowering the operating temperature without a majormodification to an existing axle assembly. To accomplish this end, anwheel is provided to rotate with the rotational members of the axleassembly and pump air to the outside of the differential. The axleassembly of the present invention further enables improved manufacturingof the axle assembly due to the simplified task of attaching the wheelto the yoke and pinion shaft during manufacture. This method furtherenables a retrofit of existing vehicles. Thus, the axle assembly of thepresent invention may be utilized with a wide variety of applicationsand is not intended to be specifically limited to the particularapplication recited herein.

With particular reference now to FIG. 1, an exemplary motor vehicle isshown and generally indicated by the reference numeral 10. Vehicle 10 isshown to include a body 12, an underbody 14, and a drive train 20.Referring now to FIG. 2, drive train 20 is shown to include an engine22, a transmission 24, having an output shaft 26 and a propeller shaft28 connecting output shaft 26 to a pinion shaft 30 of the rear axleassembly 32. Rear axle assembly 32 includes an axle housing 34, adifferential assembly 36 supported in axle housing 34, and a pair ofaxle shafts 38 and 40, respectively interconnected to the left and rightrear wheels 42 and 44. Pinion shaft 30 has a pinion shaft gear 46 fixedthereto which drives a ring gear 48 that is fixed to a differentialcasing 50 of differential assembly 36. A gear set 52 supported withindifferential casing 50 transfers rotary power from differential casing50 to output shafts 54 and 56 connected to axle shafts 38 and 40,respectively, and facilitates relative rotation therebetween. Whiledifferential assembly 36 is shown in a rear wheel drive application, thepresent invention is contemplated for use in differential assembliesinstalled in transaxles for use in front wheel drive vehicles and/or intransfer cases for use with four wheel drive vehicles.

Referring now to FIGS. 3 and 4, axle assembly 32 is described in detail.Differential assembly 36 is a parallel axle type that includes a axlehousing 34 defining an internal chamber 58 with a lubricating fluid 60contained therein. Pinion shaft 30 connects to propeller shaft 28 via ayoke 62 that is operably connected to pinion 30 for rotation therewith.An wheel 66 is interposed between differential assembly 36 and yoke 62such that wheel 66 is coupled for rotation with yoke 62 and pinion shaft30. In the particular example provided, wheel 66 is bolted to pinionshaft 30 and yoke 62, but those skilled in the art will appreciate thatwheel 66 could be coupled to pinion shaft 30 and/or yoke 62 in anyappropriate manner. Axle housing 34 includes an inside surface 70 and anoutside surface 72. Lubricating fluid 60 is in contact with ring gear 48and gearset 52 and receives heat therefrom. Lubricating fluid 60 is incontact with inside surface 70 of axle housing 34 for transfer of heatthereto.

During operation of vehicle 10 the internal moving components of axleassembly 32, including gearset 52, pinion shaft gear 46, and ring gear48, produce heat. This heat is transferred to lubricating fluid 60 andthen transferred to axle housing 34, via inside surface 70, and then outaxle housing 34 through outside surface 72. The amount of heat removedfrom outside surface 72 depends upon the volumetric airflow across axlehousing 38. As vehicle 10 is moving, airflow across outside surface 72results in forced air convection, which can be supplemented with the airsupplied by wheel 66, as discussed below. While axle housing 34 is shownto include a smooth outer outside surface 72, it would be appreciatedthat outside surface 72 could be provided with fins that could add tothe structural stiffness and/or heat dissipation capability of outsidesurface 72.

With reference now to FIGS. 5-7, wheel 66 is described in greaterdetail. Wheel 66 is shown to include a cylindrical outer surface 80, anannular leading surface 82, an annular trailing surface 84 and an innercylindrical surface 86 defining a central bore 88. As best seen in FIG.7, wheel 66 further includes a partial cylindrical bore 90 thatintersects leading surface 82 and forms a recessed cylindrical surface92 and a recessed annular surface 94. Mounting apertures 96 are formedwithin wheel 66 from recessed surface 94 to trailing surface 84.Mounting apertures 96 are provided for attachment of wheel 66 to yoke 62and/or pinion shaft 30.

Wheel 66 is further shown to include at least one duct 100 formedtherein. Duct 100 is defined by a leading edge 102, a lip 104, a ramp106, ramp walls 108, and an outlet 110. Outlet 110 defines an aperturewithin trailing surface 84. Leading edge 102, lip 104, and ramp walls108 intersect leading surface 82 to define an opening 112. While outersurface 80 is illustrated as a cylindrical surface, it would beappreciated that outer surface 80 could be other shapes, such asfrusto-conical or a plurality of intersecting polygons, depending uponthe relative geometry of leading surface 82 and trailing surface 84.

Duct 100 is shown in FIGS. 5-7 to be a variable area duct such asdetailed in National Advisory Committee for Aeronautics (NACA), AdvanceConfidential Report 5120 of Nov. 13, 1945, declassified version datedJul. 3, 1951, “An Experimental Investigation of NACA, Submerged-DuctEntrances.” The geometry of duct 100 is formed to allow duct 100 toperform similar to a variable geometry NACA duct as discussed herein.

Referring now to FIGS. 8 and 9, a streamline body 120 is illustrated toinclude an outer surface 124 with a NACA duct 130 formed therein. NACAduct 130 is defined by a leading edge 132, a lip 134, a ramp 136, a pairof ramp walls 138 and a centerline C. The distance between leading edge132 and lip 134 along centerline C is illustrated as length L. Lip 134has a width W. Ramp walls 138 and ramp 136 are formed to converge asthey approach lip 132. Thus formed, the cross-sectional area of duct 130taken normal to centerline C increases from leading edge 132 to lip 134.

Laminar air flow in the direction of arrow F across streamline body 120creates a boundary layer of air immediately adjacent streamline body120. As the boundary layer encounters the leading edge 132 of NACA duct130, the flow area available to the boundary layer increases. Thisincrease in flow area provides a localized reduction in air pressurewithin the boundary layer. As the boundary layer continues to flow alongthe length L of the NACA duct 130 from the leading edge 132 to the lip134, the curvature of the ramp walls 138 and the angle of the ramp 136relative the outer surface 134 of the streamline body 120 create afurther increase in flow area available to the boundary layer of air anda resulting further decrease in localized air pressure within theboundary layer. This decreased localized air pressure zone is defined bythe air within the duct and immediately adjacent the duct opening. Thisdecrease in air pressure results in an increase in air velocity. Theresulting low pressure acts to draw or suck air into the duct openingformed in the outer surface 124 by creating a vacuum effect. The airdrawn into duct 130 is then directed to a preselected air intake, suchas an engine intake or cooling surface.

The vacuum effect does not impart a significant amount of turbulence inthe boundary layer. In contrast, an air scoop that is positioned intothe path of the boundary layer will divert air into an opening in asurface of a streamline body by pushing the air into the surfaceopening. This pushing of air, however, creates a reactive force withinthe scoop and creates drag in the boundary layer as turbulence isimparted to the boundary layer downstream of the scoop along thestreamline body. Thus provided, a conventional NACA duct 130 draws in aportion of air from a boundary layer as the boundary layer of air passesthe opening of the NACA duct 130, thus diverting air with negligibleturbulence. The present invention utilizes this vacuum creating effectto suck air into ducts 100, as described below. As illustrated, NACAduct 130 is symmetrical along centerline C, although it will beappreciated by one skilled in the art that a duct need not besymmetrical to operate in the manner described above.

As best seen in FIGS. 5 and 6, the direction of travel, as indicated byarrow T, of vehicle 10 provides a resultant airflow generally in thedirection of arrow A. This airflow impacts leading surface 82 and buildsa resulting air pressure gradient along leading surface 82 with a higherpressure found adjacent lead surface 82. Layers of air adjacent leadingsurface 82 are represented as L1, L2, and L3, wherein the air pressurewithin layer L1 is greater that the air pressure within layer L2, andthe air pressure within layer L2 is greater that the air pressure withinlayer L3. Travel of vehicle 10 in direction T also results in rotationof wheel 66 in the direction shown in FIG. 5. As best seen in FIGS. 5and 7, duct 100 is formed in wheel 66 such that leading edge 102 isfollowed by lip 104 as wheel 66 rotates in the direction of arrow R. Aswheel 66 rotates, ducts 100 create locations of localized low pressurewithin openings 112, in the same manner as discussed above withreference to the operation of a NACA duct 130. These locations oflocalized low pressure pull air from layer L1 into openings 112.Rotation of wheel 66 allows ducts 100 to draw in air which is expelledthrough outlets 110 and onto outside surface 72 of axle housing 34. Thisdecrease in pressure within ducts 100 results in an increase in velocityfor a gas such as air. This increase in velocity of air provides for alarger volumetric air flow directed to exterior surface 72 of axlehousing 34 thereby providing a greater amount of heat dissipation fromaxle assembly 32. Further travel of vehicle 10 causes further rotationof wheel 66 and additional air to encounter leading surface 82. Thisfurther rotation of wheel 66 draws the additional air into ducts 100.Thus provided, wheel 66 provides a device useful to draw air andincrease the velocity of the air to provide a greater cooling capacityto an existing assembly.

Referring now to FIG. 10, an alternate embodiment of wheel 66 is shownas an wheel 266 including a plurality of ducts 200, a cylindrical outersurface 280, an annular leading surface 282, and an annular trailingsurface 284. Each duct 200 is defined by a leading edge 202, a lip 204,a ramp 206, ramp walls 208, and an outlet 210 that intersects trailingsurface 284. Leading edge 202, lip 204, and ramp walls 208 intersectleading surface 282 to define an opening 212. Opening 212 has agenerally oval cross section and ramp 206 is curved and integral withramp walls 208. Wheel 266 operates in a manner similar to wheel 66 asdiscussed herein.

While ducts 100, 130 and 200 are illustrated with specific geometries,it would be appreciated by one skilled in the art that a duct of anyother geometry within an wheel that is designed to draw air into theduct from an adjacent air layer could be utilized to produce a similarresult.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

The curvature of ramp walls 138 relative the centerline C of NACA duct130 is represented in Table 1 wherein the relationship between adistance x along centerline C from lip 134 and a corresponding distancey is tabulated. Distance y is the distance from the centerline C atdistance x to the ramp walls 138. TABLE 1 x/L y/B 0.0 0.500 0.05 0.49300.10 0.4670 0.20 0.3870 0.30 0.3100 0.40 0.2420 0.50 0.1950 0.60 0.15500.70 0.1200 0.80 0.0750 0.90 0.0575 1.00 0.0440

1. A vehicle driveline component comprising: a housing defining achamber; a power transfer mechanism rotatably disposed within thehousing, the power transfer mechanism including a shaft, wherein theshaft is rotatably mounted within the housing; and a wheel rotatablyconnected to the shaft having a leading surface and a trailing surface,wherein a duct is formed within the wheel, wherein the duct has anintersection with the leading surface and the trailing surface, and theduct is adapted to draw a fluid therethrough during rotation of thewheel.
 2. The vehicle driveline assembly of claim 1, wherein the wheelis positioned adjacent the axle assembly to direct air onto the outersurface of the housing.
 3. The vehicle driveline assembly of claim 1,wherein the power transfer mechanism is a differential assembly.
 4. Thevehicle driveline assembly of claim 3, wherein the vehicle drivelinecomponent is an axle assembly.
 5. The vehicle driveline assembly ofclaim 1, wherein the wheel comprises a plurality of ducts formedtherein.
 6. The vehicle driveline assembly of claim 1, wherein the ductis a NACA duct.
 7. The vehicle driveline assembly of claim 1, whereinthe leading surface is generally annular.
 8. The vehicle drivelineassembly of claim 1, wherein the trailing surface is generally annular.9. The vehicle driveline assembly of claim 1, wherein the intersectionof the leading surface and the duct is generally triangular.
 10. Thevehicle driveline assembly of claim 1, wherein the intersection of theleading surface and the duct is generally oval.
 11. The vehicledriveline assembly of claim 1, wherein the intersection of the trailingsurface and the duct is generally rectangular.
 12. The vehicle drivelineassembly of claim 1, wherein the intersection of the trailing surfaceand the duct is generally circular.
 13. The vehicle driveline assemblyof claim 1, wherein a plane including the leading surface is generallyperpendicular to an axis of the shaft.
 14. An wheel comprising: agenerally solid body bounded by an annular leading surface, an annulartrailing surface, and an outer surface, wherein the leading surface andthe trailing surface are generally parallel, the body having a centralbore and a plurality of radially spaced apertures extending therethroughfrom the leading surface to the trailing surface wherein the centralbore is adapted to restrain the wheel for rotation with a shaft and theradially spaced apertures are adapted to draw a fluid therethroughduring said rotation.
 15. The wheel of claim 14, wherein across-sectional area of each duct, taken normal to the leading surfaceand intersecting a radius of the wheel, is variable as the radius isrotated along an arc defining the annular leading surface.
 16. Themethod of claim 14, wherein forming the wheel includes forming aplurality of variable area ducts therein.
 17. The method of claim 14,wherein forming the wheel includes forming a plurality of ducts therein,wherein the cross-sectional area of each duct, taken normal to theleading surface and intersecting a radial line of the wheel, is variableas the radial line is rotated within a plane defined by the leadingsurface.
 18. The method of claim 17, wherein each duct is configured tocreate a vacuum during said rotating.
 19. The method of claim 14,further comprising: directing the air onto a surface of the axleassembly.
 20. The method of claim 14, wherein rotating the wheel doesnot push air into an inlet of the wheel.